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Discussion Starter #1
Hi everyone

I've posted before about uncomfortably high ATF temperatures when towing up an extended 6.25% grade in 90 degree whether. One thing I noticed at the time was that the cooling fans didn't seem to come on until the coolant temperatures hit ~208 degrees. (I didn't run the A/C going up the hill for hopefully obvious reasons, although this would have triggered the fans at low speed). It occurred to me that having the fans come on sooner would bring down the coolant temperature and therefore also make a noticeable difference in the ATF temperature, considering that the ATF runs through the OTW cooler in the radiator, and that the heat builds up slowly over time.

I looked at the cooling fans circuit on pg. 10-18 of the shop manual, and noticed in steps 4 & 5 of the Radiator Fan High Speed Circuit Troubleshooting section on the following page, and in step 4 of the A/C Condenser Fan High Speed Circuit Troubleshooting section on page 21-69, that it was possible to run both of these fans by jumping the appropriate socket terminals of the relays. I gave it a quick try, and the fans came on nice & strong.

So my thought was that the next time I would proceed as usual up until the big grade, at which point I would stop, jump the appropriate relays, and climb the hill with both fans going at high speed (A/C off). I don't see any reason why this would be a problem, but that's not the same as flatly saying there is no problem, so I'd like to put the question to the experts here.

Is there any reason why this would be inadvisable?

Thanks everyone!
 

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Maybe include a link to your other post in this one? I'm not sure what you consider excessive but anything up to and a little over the engine coolant temp (so 210 to say 230, some even say up to 250) is normal operating range for ATF, it doesn't start breaking down until beyond that... If you are uncomfortable taking "the internet's word" on that, give your ATF supplier (I use Valvoline MaxLife) a call and they can tell you what temperature you need to be concerned at...

Regarding your "precooling" concept, it sounds good in theory BUT, what speeds are you traveling at the time? The cooling fans become less effective as speed increases, they should shut off after a certain MPH that the engineers set during the design phase.

Have you considered installing a larger, separate ATF cooler? I think that would be my first move to allow for slightly higher ATF capacity and so the ATF operates independently of the coolant temperature...
 

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Discussion Starter #3
Thanks a bunch, cintocrunch!

Maybe include a link to your other post in this one?
You're right. Was thinking of doing that last night but was late for bed. Here it is!

I'm not sure what you consider excessive but anything up to and a little over the engine coolant temp (so 210 to say 230, some even say up to 250) is normal operating range for ATF, it doesn't start breaking down until beyond that... If you are uncomfortable taking "the internet's word" on that, give your ATF supplier (I use Valvoline MaxLife) a call and they can tell you what temperature you need to be concerned at...
Thanks, this is really useful. You have no idea how hard I've tried to get some numbers, but most of what I've found seems to be geared to selling tranny coolers. To answer your question, I peaked at just over 230 (see link above). I also just read on this forum that the transmission temperature idiot light doesn't come on until 290, which seems to back you up. However my concern has less to do with degrading the fluid (I have no problem changing it frequently), and more with degrading the transmission itself, particularly the seals. But I suspect that 230 for short periods shouldn't take much life out of the tranny, particularly if it otherwise runs on the cool end & I change fluid regularly.


Regarding your "precooling" concept, it sounds good in theory BUT, what speeds are you traveling at the time? The cooling fans become less effective as speed increases, they should shut off after a certain MPH that the engineers set during the design phase. I go up the grade at about 45. I think at that speed they are still effective, considering they arrested the rise in coolant temperature at ~208.

Have you considered installing a larger, separate ATF cooler? I think that would be my first move to allow for slightly higher ATF capacity and so the ATF operates independently of the coolant temperature...
I actually did install an aftermarket cooler (679) a few weeks ago, but so far it raised more questions than answers. The outfit I bought it from said to bypass the OTW cooler in the radiator. In city driving the ATF temp is now a bit higher than with the Honda HD cooler. In theory it could keep the ATF temp down far enough when towing assuming the fluid comes out of the tranny at a lower temp than the radiator coolant, but I am skeptical of this, so I'll probably put it back in series with the OTW cooler in the rad. All of which brings me back to trying to keep the coolant temperature down by jumping the fan relays. I suppose I'll keep that in my back pocket.

BTW, I was going to start a separate thread about my experience installing that cooler, but for the moment a picture will suffice.


Thanks again!
 

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Thanks a bunch, cintocrunch!

Maybe include a link to your other post in this one?
You're right. Was thinking of doing that last night but was late for bed. Here it is!

I'm not sure what you consider excessive but anything up to and a little over the engine coolant temp (so 210 to say 230, some even say up to 250) is normal operating range for ATF, it doesn't start breaking down until beyond that... If you are uncomfortable taking "the internet's word" on that, give your ATF supplier (I use Valvoline MaxLife) a call and they can tell you what temperature you need to be concerned at...
Thanks, this is really useful. You have no idea how hard I've tried to get some numbers, but most of what I've found seems to be geared to selling tranny coolers. To answer your question, I peaked at just over 230 (see link above). I also just read on this forum that the transmission temperature idiot light doesn't come on until 290, which seems to back you up. However my concern has less to do with degrading the fluid (I have no problem changing it frequently), and more with degrading the transmission itself, particularly the seals. But I suspect that 230 for short periods shouldn't take much life out of the tranny, particularly if it otherwise runs on the cool end & I change fluid regularly.


Regarding your "precooling" concept, it sounds good in theory BUT, what speeds are you traveling at the time? The cooling fans become less effective as speed increases, they should shut off after a certain MPH that the engineers set during the design phase. I go up the grade at about 45. I think at that speed they are still effective, considering they arrested the rise in coolant temperature at ~208.

Have you considered installing a larger, separate ATF cooler? I think that would be my first move to allow for slightly higher ATF capacity and so the ATF operates independently of the coolant temperature...
I actually did install an aftermarket cooler (679) a few weeks ago, but so far it raised more questions than answers. The outfit I bought it from said to bypass the OTW cooler in the radiator. In city driving the ATF temp is now a bit higher than with the Honda HD cooler. In theory it could keep the ATF temp down far enough when towing assuming the fluid comes out of the tranny at a lower temp than the radiator coolant, but I am skeptical of this, so I'll probably put it back in series with the OTW cooler in the rad. All of which brings me back to trying to keep the coolant temperature down by jumping the fan relays. I suppose I'll keep that in my back pocket.

BTW, I was going to start a separate thread about my experience installing that cooler, but for the moment a picture will suffice.


Thanks again!
I think you are seeing the dichotomy of having the trans cooler separated from the radiator... so when you need ultimate cooling it may be better as it keeps the fluids separated during high load situations but during low load situations you aren't getting the "cooling" effect of the coolant in the radiator, keeping the trans at or less than the coolant temp... very interesting observation...

IDK how hot the trans is getting under normal use, but have you considered a small thermostatically controlled fan for the trans cooler? A pusher fan that comes on at say 200 or 190 or whatever temp you set it to? Or even that one could be switched...
 

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Discussion Starter #5
Post trip follow-up...

First of all, I'm still learning about Automatic transmissions & ATF (all my previous vehicles have been Manuals), and I based on what I have been reading since, I suspect that most modern fluids & trannys can easily deal with higher than 230 degrees. That being said...

As long as I had the jumpers made, I used them this last August on our annual trip. I pulled off the highway right before the big push (or should I say pull) up the hill, and put them in. Then I let the fans run for a few minutes to pull the engine & tranny temp down a bit before I started up the hill. The ATF temp topped out at 215 this time, and the engine coolant never even got up to 190.0. Of course I don't know whether the outside temperature was hotter or not, but it felt like it was close to the same. And when I got to the top, it all cooled off much quicker.

And since everything else was cooler, so was I!

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